1. Field of the Invention
This invention relates to a method for acquiring azimuth information using signals transmitted from GPS (global positioning system) satellites.
2. Description of the Prior Art
Previously, positioning information such as latitude, longitude, altitude and GPS (Global Positioning System) time were readily obtainable from signals transmitted by GPS satellites but azimuth information could not be acquired.
The inventor therefore developed a method for acquiring azimuth information by use of a pair of planar patch antennas (Japanese Patent Application Nos. 2000-91362 and 2001-93964).
This method for acquiring azimuth information includes a step of disposing a pair of planar patch antennas back-to-back, parallel to each other and vertical, whereby each planar patch antenna forms a sky coverage area of antenna sensitivity that is a sky quarter-sphere in the direction the antenna faces; a step of causing receiver units connected to the respective antennas to extract strength values of all received GPS satellite signals; a step of discriminating based on a comparison of the extracted signal strength values the antenna in whose sky coverage area the GPS satellite that transmitted each signal is present; a step of arranging the results of the step of discriminating areas of satellite presence in a ring-like sequence; and a step of determining or limiting an azimuth of a measurement direction based on information contained in a ring-like discrimination results sequence.
In order to implement this method for acquiring azimuth information in a commercially available GPS receiver, the inventor further developed a GPS receiver including a data transmitting unit, a data receiving unit and a data processing unit (Japanese Patent Application No. 2000-364605).
This made it possible to readily acquire azimuth information by disposing a pair of planar patch antennas back-to-back, parallel to each other and vertical, disposing a pair of GPS receivers so that the data transmitting unit and data receiving unit of each GPS receiver faces the data receiving unit and data transmitting unit of the other, thereby enabling GPS satellite data received by one GPS receiver to be transmitted to the other GPS receiver, and processing the two sets of data with the data processing unit.
Azimuth information acquired from GPS satellite signals is more reliable than azimuth information acquired using a compass that is affected by magnetic fields.
However, the foregoing method for acquiring azimuth information proposed by the inventor requires two planar antennas to be disposed in parallel and the data acquired by one of the GPS receivers to be transmitted to the other. It therefore requires at least two antennas and means for transmitting data between the two GPS receivers.
The present invention was accomplished in light of the foregoing circumstances and has as an object to provide a very simple method for acquiring azimuth information that enables acquisition of azimuth information with only a single planar antenna and a single GPS receiver.
This invention achieves this object by providing a method for acquiring azimuth information comprising:
a step of disposing a single GPS planar antenna having a hemispherical antenna pattern with its beam center horizontal to form a sky coverage area of antenna sensitivity that is a sky quarter-sphere in the direction the GPS antenna faces bounded by a great semicircle passing through the zenith;
a step of causing a GPS receiver connected to the GPS antenna to attempt reception of signals transmitted by GPS satellites in the sky hemisphere;
a step of discriminating from the received signals the satellites present in the coverage area;
a step of using azimuths of the satellites obtained by a positioning calculation process to arrange the satellites found to be present in the sky coverage area in clockwise order as viewed from the sky coverage area start azimuth; and
a step of limiting the azimuth of a direction in which one side of the great semicircle faces within an azimuth range defined clockwise whose start azimuth is the azimuth of the satellite corresponding to the last in said order and whose end azimuth is the reverse direction from the azimuth of the satellite corresponding to the first in said order.
In one aspect of the present invention, the method further comprises:
a step of turning the GPS planar antenna 180 degrees;
a step of causing the GPS receiver connected to the GPS antenna to attempt reception of signals transmitted by GPS satellites in the sky hemisphere and limit the azimuth of the direction in which the other side of great semicircle faces by the same steps as set out above; and
a step of limiting a single azimuth by taking the common product of sets of the azimuth obtained in the first GPS antenna attitude and the azimuth obtained in the second GPS antenna attitude.
In another aspect of the present invention, the method further comprises a step of mounting the GPS antenna on the head and putting the antenna in a horizontal state or a vertical state in accordance with information to be acquired.
As set out in the foregoing, the present invention enables acquisition of azimuth information using a single GPS antenna having a hemispherical antenna pattern and is therefore extremely simple and economical.